1. Field of the Invention
The present invention relates to a capacitor of an integrated circuit device and a method of manufacturing the same. More particularly, the present invention relates to a metal-insulator-metal capacitor of a semiconductor memory cell such as a dynamic random access memory cell, and a method of manufacturing the same, in which oxidation of a contact plug during deposition of a dielectric material having a high dielectric constant to form a dielectric layer is prevented.
2. Description of the Related Art
As a degree of integration of a semiconductor memory device, such as a DRAM cell increases, it becomes more difficult to obtain a sufficient capacitance due to a resulting decrease in size of individual memory cells. Recently, various efforts have been made to obtain a sufficient capacitance from a limited cell area.
There are typically two methods to increase a cell capacitance. A first method is to use a material having a high dielectric constant as a dielectric layer of the capacitor. A second method is to increase an effective area of the cell using a hemisphere silicon grain (HSG) growing method.
As for the material having a high dielectric constant, a metal oxide layer comprised of Ta2O5, TaOxNy, Al2O3, (Ba, Sr)TiO3[BST], SrTiO3[ST], Pb(Zi, Ti)O3[PLZT], SBT, or like, is used instead of a silicon oxide layer or a nitride layer.
Even though the dielectric layer is formed by depositing Ta2O5 on a semiconductor substrate by a chemical vapor deposition (CVD) method, an oxygen vacancy where an oxygen bonding is absent is inevitably present in the dielectric layer. Therefore, a UV O3 treatment is typically performed to supplement the oxygen vacancy during the CVD process. Furthermore, the dielectric layer is crystallized by means of a heat treatment in an oxygen atmosphere to increase a dielectric constant after performing the deposition.
A storage node is oxidized through a reaction with oxygen when the dielectric layer comprised of Ta2O5 is subjected to the heat treatment in an oxygen atmosphere during or after the deposition thereof. Formation of an oxide layer through this oxidation process increases the thickness of the dielectric layer of the capacitor, thereby decreasing the dielectric constant, which results in a reduction in capacitance of the capacitor of the semiconductor memory cell.
Since the use of an existing polysilicon electrode is limited, a novel material for formation of an electrode and a novel structure of the electrode are required. As platinum (Pt) has a high reactivity to silicon, when platinum is used for formation of the electrode, a barrier layer is needed to insulate the platinum electrode from a contact plug comprised of polysilicon. Typically, titanium nitride or tantalum nitride is used as the barrier layer.
However, during or after deposition of a layer to form a lower electrode or a dielectric layer, a heat treatment is performed in an oxygen atmosphere to crystallize the lower electrode layer or the dielectric layer. During this heat treatment, oxygen diffuses along a boundary surface between a barrier layer and an insulation layer to reach a contact plug, resulting in oxidation of a surface portion of the contact plug. The oxidation of the contact plug decreases the capacitance of the capacitor of the semiconductor memory cell.
Hereinafter, a conventional capacitor of an integrated circuit device will be described.
FIG. 1 illustrates a sectional view showing a conventional concave type of a metal-insulator-metal capacitor of an integrated circuit device. FIG. 2 illustrates a sectional view showing a conventional convex type of a metal-insulator-metal capacitor of an integrated circuit device.
The concave type of the metal-insulator-metal capacitor of the integrated circuit device is formed in such a manner that a first insulation layer 12 is formed on a semiconductor substrate 10 and a contact plug 14 is formed in the first insulation layer 12. A diffusion barrier layer 16 comprised of a nitride material and a second insulation layer 18 are sequentially deposited on the contact plug 14. A through hole 20 is formed in the second insulation layer 18 and through the diffusion barrier layer 16. A barrier layer 22, a lower electrode layer 24, a dielectric layer 26 and an upper electrode layer 28 are subsequently formed in the through hole along a surface profile of the through hole 20.
The convex type of the metal-insulator-metal capacitor of the integrated circuit device is formed in such a manner that a first insulation layer 112 is formed on a semiconductor substrate 110 and a contact plug 114 is formed in the first insulation layer 112. A barrier layer 122 and a thick lower electrode layer 124 are integrated and subsequently formed on the contact plug 114. Then, the barrier layer 122 and the lower electrode layer 124 are patterned by a photolithography so that each node is defined. Subsequently, a dielectric layer 126 and an upper electrode layer 128 are sequentially stacked on the lower electrode 124.
In FIGS. 1 and 2, when the dielectric layers 26 and 126 are crystallized under an oxygen atmosphere, oxygen diffuses toward an upper portion of the contact plugs 14 and 114 along oxygen diffusion pathways 30 and 130 on a boundary surface between the barrier layers 22 and 122 and the insulation layers 12 and 112. As a result, the contact plugs 14 and 114 formed of polysilicon make contact with oxygen at the upper portion thereof to be oxidized and converted into silicon oxide layers 32 and 132, which act as an insulator. This increases a contact resistance between the lower electrode and the plug of the capacitor thereby decreasing reliability of the cell capacitor.
From FIGS. 1 and 2, it may be noted that since the convex type of the capacitor of the integrated circuit device has a shorter oxygen diffusion pathway 130 than the oxygen diffusion pathway 30 of the concave type of the capacitor of the integrated circuit device, the convex type of the capacitor of the integrated circuit device has a weaker structure. Accordingly, the plug of the convex type capacitor is more easily oxidized due to the diffusion of oxygen than the concave type capacitor of the integrated circuit device.
Furthermore, in the concave type metal-insulator-metal capacitor, the nitride layer 16 is disposed between the first insulation layer 12 and the second insulation layer 18 to prevent the diffusion of oxygen.
However, although the nitride layer acts to substantially reduce the oxidation of the upper portion of the plug, the nitride layer cannot completely prevent oxidation of the plug.
That is, it is difficult to prevent oxidation of the plug because the nitride layer as the diffusion barrier layer is not sufficiently dense, and a distance between the nitride layer and the upper portion of the plug is very short.